Positioning systems for objects such as moving vehicles come in a variety of well-known configurations. For example, a global navigation satellite system (GNSS) such as the well-known US Global Positioning System (GPS), the Russian GLONASS or European GALILEO, utilize radio frequency signals and other location information received from satellites for providing outdoor location and positioning with a high degree of accuracy. However, these satellite signals become weak and attenuated for indoor applications due to their line-of-sight requirements and GPS devices, for example, have a difficult time locking onto such signals when operating indoors. Further, for example, construction vehicles operating inside a large building or domed stadium structure (on the scale of 100 meters wide and tens of meters high) require the use of robotic total stations in performing construction work and these large-scale indoor structures are, in terms of using GNSS signals, susceptible to multi-path propagation effects, power loss as GNSS signals pass through construction materials, and electromagnetic and audio interference thereby making indoor positioning a challenge using GNSS signals.
As such, a variety of positioning techniques exist to facilitate indoor positioning and alleviate some of the above-detailed disadvantages with respect to using GNSS signals for indoor applications. For example, certain techniques utilizing received signal strength indication (RSSI) from Wi-Fi and Bluetooth® wireless access points have been identified, however, complex indoor environments cause these types of radio waves to propagate in dynamic and unpredictable ways thereby limiting the overall positioning accuracy using RSSI.
Another indoor positioning alternative utilizes ultrasonic sonar which transmits acoustic waves to microphones in order to approximate indoor positions. This alternative technique operates at lower frequencies than Wi-Fi based systems and attenuate significantly when passing through walls, for example, thereby potentially increasing positioning accuracy.
A further positioning technique uses optical signals, either visible or infrared, which tend to have better accuracy than RSSI and/or ultrasonic sonar given that optical signals are highly directional and do not penetrate solid objects. Such optical techniques may use well-known light identification detection and ranging (LIDAR) which is a remote sensing method, similar to radar, that uses a laser pulse transmitted by a transmitter and the light particles (photons) are scattered back to a receiver and examined for position determination. Markers and landmarks may also be used where markers are active if they contain a transmitter emitting light or passive if the reflected ambient light is utilized, and/or a landmark position can be predetermined (or determined in real-time using the well-known simultaneous localization and map building (SLAM) technique). Nevertheless, the directionality of such optical signals limits their potential reliability in certain operating environments given the necessity to properly align the receiver and transmitter associated with the optical signals.
Therefore, a need exists for an improved technique for indoor vehicular positioning within large-scale structures.